MR heads have the potential of being built to accommodate very narrow track widths both for tape and disk applications. A key requirement for any read head is that the amplitude of the read signals be reasonably large relative to the background electronic noise. Progress toward narrow tracks inevitably reduces the read signal amplitude because of the reduced amount of flux that enters the head. Ultimately this trend sets the limits to achievable track densities. The present invention increases the read signal amplitudes and thereby facilitates the reading of tapes or disks and the like (hereinafter tapes) with narrower tracks.
It is known to position an MR element between two magnetic pole pieces which function as a read head when magnetic material, such as a tape, is passed over the gap defined by the spacing between the pole pieces. In order to provide MR heads having a high signal sensitivity, and hence the capability of reading high density data, it is important that an optimum flux path be provided within the MR element. This generates the greatest possible output signal from the MR element as it responds to flux changes.
In prior art heads, the MR element is positioned in parallel between two parallel mating faces of the magnetic pole pieces. When a magnetic tape passes over the head gap on a read operation, it is the flux that emanates from the tape and enters the MR element that causes the MR element to change its resistance and generate an output signal representing the detected flux. If this output signal is to be of the largest possible amplitude for a given flux level (high signal sensitivity), it is necessary that this flux travel a maximum distance within the MR element. Flux enters the top of the MR element and travels downwards within the MR element and then returns via a magnetic pole piece to the tape.
FIG. 1 shows a prior art head 100 of this type as comprising a first magnetic pole piece 101 having a mating surface 107, an insulator 103 affixed to mating surface 107, an MR element 105 affixed to insulator 103, an insulator 108 and a second magnetic pole piece 102 having a mating surface 106.
Head 100 operates in such a manner that as tape 109 passes over the pole piece gap, flux emanates therefrom and enters the top of MR element 105. Only that portion of the flux that enters the MR element is effective in generating an output signal. The total flux F that emanates from the tape comprises the various sub-elements F1, F2, F3 . . . Fn. Flux element F1 enters the MR element and travels downward only a short distance before it leaks through insulator 103, enters pole piece 101 and returns to tape 109. Flux element F1 generates some, but not much, of the output signal of MR element 105. Flux element F2 travels downward somewhat further within MR element 105 before it jumps through insulator 103 and returns via pole piece 101 to tape 109. Flux element F2 generates a somewhat greater output signal in MR element than does flux element F1. Flux element F3 travels downward further within MR element 105 before it returns via insulator 103 and pole piece 101 to tape 109. It is more effective in generating an output signal per unit of flux than are flux elements F1 and F2. The flux element Fn travels downward through the entirety of MR element 105 before it returns to pole piece 101 and tape 109. This maximum length of flux travel for flux element Fn within MR element 105 causes it to be the most effective in generating an output signal in MR element 105.
The efficiency of the various portions of MR element 105 decreases with downward flux travel through MR element 105. The MR element is the most effective at its top portion in FIG. 1 since all of the flux that enters the element travels therethrough and is effective to generate an output signal. However, the efficiency rapidly decreases with downward travel toward its inner edge since most of the flux leaks through insulator 103 and returns to tape 109 rather than traveling downward the entire length of MR element 105. The average flux density is thus less than 50% of the entering flux density and the effectiveness of the output signal is similarly decreased. The MR heads of the prior art thus have an inherent limitation that their flux efficiency is less than 50% as compared to the flux density at the outer or top portion of the MR element. This 50% limitation causes a corresponding decrease in the output signal generated by the heads and thereby makes more difficult the reading of data on narrow tracks.
It is therefore a problem for the prior art MR heads to read data and signals on tracks of narrow width. This limits the progress of the industry toward increasingly narrow tracks and higher density data on tapes and disks.